Unit 12: Nervous Control Chapter 25

The Role of the Nervous System Which characteristic of life is an organism’s nervous system related to? Receives information from internal and external stimuli – and responds (by sending a message to an “effector” such as a muscle or gland)

Nervous Response 4 requirements before nervous response can occur: Detection of stimulus by sensory receptors Transmission of impulse along neurons Interpretation & analysis of impulses in coordination center brain or spinal cord Response by effectors muscles or glands 4 requirements must be met before nervous response can occur: Detection of stimulus by sensory receptors (Ex. touch-sensitive cells in skin or cells that form part of sense organ such as eye or ear) convert input into electrical impulse Ex. Touch hot stove & sense too much heat Transmission of impulse to other parts of body along network of neurons (which are specialized cells for conducting nerve impulses) Ex. signal sent along sensory neurons to brain or spinal cord Interpretation & analysis of impulses which take place in coordination center (brain or spinal cord) Ex. brain or spinal cord interprets & processes signal in interneuron Appropriate response by effectors (Muscles or glands that cause the actual response to the stimulus.) Ex. motor neurons transmit outgoing impulses to the effectors which respond (pull hand away from hot stove)

Nerve Tissue Nerve Neurons many neurons bundled together specialized cells that transmit nerve impulses through body different types sensory neurons interneurons motor neurons Different types of neurons differ in structure & direction in which they carry impulses

Different Types of Neurons Sensory neurons transmit impulses from receptors to coordination center Interneurons transfer impulses from sensory to motor neurons in brain & spinal cord Motor neurons transmit outgoing impulses to effectors Sensory neurons transmit incoming impulses from receptors to a coordination center where impulses are interpreted Interneurons transfer impulses from sensory to motor neurons (in brain & spinal cord) Motorneurons once incoming impulses have been analyzed, the brain or spinal cord will send out a response… motor neurons transmit outgoing impulses to effectors

Neuron Structure dendrites cell body axon conduct impulses toward cell body cell body resembles other types of cells contains nucleus & cytoplasm axon carries impulses away from cell body often covered with myelin sheath end branch dendrites highly branched fibers; receive impulses from end brush of previous neuron; conduct impulses toward cell body cell body portion of neuron that most resembles other types of cells…. contains nucleus & cytoplasm Axon long, narrow portion of cell; carries impulses away from cell body… to end brush (end of axon that divides into many filaments… then impulse travels to dendrites of next neuron or to effector). Axons are often covered with myelin sheath (insulating lipid material). Myelin allows impulse to move very rapidly… consists of many layers… made of Schwann cells wrapping around & around axon… Schwann cells help provide nourishment to the axon & aids in axon regeneration. Between Schwann cells the axon is left uncovered. These bare areas are called nodes of Ranvier & help transport impulses quickly b/c the impulse is able to move from node to node instead of continuously along membrane.

Neuron Structure dendrites terminal buttons (end branch) nucleus cell body (soma) axon terminal buttons (end branch) cytoplasm nucleus dendrites myelin sheath nodes of Ranvier

Transmitting Impulses Along a Neuron nerve impulse or “action potential” results from changes in ion concentration inside/outside neuron plasma membrane

Transmitting Impulses from Neuron to Neuron between each neuron is a synapse small fluid-filled space neurotransmitters (chemicals) help impulse across synapse Virtually all nerve impulses must travel through many neurons before reaching their targets Impulse is transmitted in only one direction

Nervous Systems In bilaterally symmetrical animals the nervous system is divided into 2 parts central nervous system (CNS) peripheral nervous system (PNS) CNS serves as control centers… info brought from PNS analyzed by means of interneurons in the CNS & impulses then carried to appropriate effectors by motor neurons of PNS PNS sensory & motor neurons connected to the CNS…. Info about animal’s environment gathered by receptors & brought to CNS by sensory neurons

Coordination between the PNS & the CNS receptors in PNS gather info about animal’s environment impulses along the PNS’s sensory neurons travel to CNS in CNS (brain & spinal cord) impulses are interpreted & analyzed impulses leaving CNS by motor neurons of PNS are carried to effectors which carryout response CNS serves as control centers… info brought from PNS (sensory neurons) analyzed by means of interneurons in the CNS & impulses then carried to appropriate effectors by motor neurons of PNS PNS sensory & motor neurons connected to the CNS…. Info about animal’s environment gathered by receptors & brought to CNS by sensory neurons

3 Major Parts of the Brain cerebrum speech, reasoning, emotions cerebellum controls balance, posture, muscle tone medulla (oblongata) controls involuntary actions of internal organs heart rate, breathing rate, peristalsis, etc. Cerebrum… sensory inputs are interpreted & motor impulses started Cerebellum… coordinates impulses sent out from cerebrum think of Belle dancing w/ the Beast…. Her balance, posture, muscle tone…. Medulla oblongata… part of brain stem…

What are reflexes? reflexes = involuntary/automatic responses to stimuli Involve CNS, but require no conscious control or decision making b/c determined by fixed pathways some through brain (ex. blinking) others through spinal cord (ex. touch hot iron & respond)

Reflexes: Initial Response & Reflex Arc Reflex Arc Animation Reflex Arc Animation 2 Reflex arc Receptors activated Sensory neuron transmits impulse towards spinal cord Impulse crosses synapse to interneuron in spinal cord Impulse crosses synapse to motor neuron & leaves spinal cord Impulse activates effectors which respond appropriately Does NOT involve brain Reflex arc Receptors activated (ex. feel excess heat) Sensory neuron transmits impulse towards spinal cord Impulse crosses synapse to interneuron in spinal cord Impulse crosses synapse to motor neuron & leaves spinal cord Impulse activates effectors which respond appropriately (ex. pull hand away) Does NOT involve brain Takes a fraction of a second

1. Sensory receptor activated (receives stimulus) 2. Sensory neuron transmits impulse towards spinal cord 4. motor neuron transmits impulse away from spinal cord 3. Impulse crosses synapse into interneuron where interpreted & analyzed Reflex arc Receptors activated (ex. feel excess heat) Sensory neuron transmits impulse towards spinal cord Impulse crosses synapse to interneuron in spinal cord Impulse crosses synapse to motor neuron & leaves spinal cord Impulse activates effectors which respond appropriately (ex. pull hand away) CNS serves as control centers… info brought from PNS (sensory neurons) analyzed by means of interneurons in the CNS & impulses then carried to appropriate effectors by motor neurons of PNS PNS sensory & motor neurons connected to the CNS…. Info about animal’s environment gathered by receptors & brought to CNS by sensory neurons 5. Impulse received by effector (which responds appropriately)

Reflex Arc Interneuron = association nerve

Reflexes: Secondary Response Since reflex actions (arcs) don’t involve the brain, how does your brain become aware? Some spinal cord interneurons that receive sensory impulses connect w/ other neuron pathways leading to the brain Brain becomes aware of what has happened Secondary response occurs You yell, “Ouch!”

Comparison of Nervous Systems

Nervous Systems in Unicellular Organisms Euglena Light-sensitive structure under the “eye-spot” Allows Euglena to swim in direction of light Paramecium Can respond to obstacles in path Turns 30 & moves forward again… Continues to do this until passes object Seems to be mainly under chemical control

Nervous Systems in Invertebrates Radially symmetrical organisms have no center for nervous control Many short neurons form nerve net No definite nerve pathways Ex. Hydra Bilaterally symmetric animals have a primitive control center(s) (ganglia) & specific nerve pathways Ex. Planaria

Nervous Systems in Invertebrates Other bilaterally symmetric animals also have brains Ex. earthworm cerebral ganglia (slightly larger ganglia) Ex. grasshopper Brain divided into specialized areas protocerebrum deutocerebrum In arthropods such as the grasshopper, the brain is divided into specialized areas, including the protocerebrum (controlling vision) and the deutocerebrum (processing antenna signals). The stomatogastric system regulates digestion.

Nervous System in Fish Lateral line system Electrical sense can sense the slightest movements (vibrations) in water Electrical sense Ampullae of Lorenzini sense changes in electrical fields Being highly complex life forms fish need a brain and a nervous system to control their body's actions. The nervous system of fish, much like ours, is composed of a central co-ordinating brain, a spinal cord and many, many nerves. The Brain:- Generally speaking fish have small brains in relationship to their overall body weight. Elasmobranchs (Sharks and Rays) in general have a slightly larger brain for the same body mass as Teleosts (Bony Fish), however there is great variety within the teleosts scientists have learned something quite surprising about the Elephantnose Fish (Gnathonemus petersii).

Questions to Ponder & Extras How do we see unity within diversity in relation to nervous control??? How does form follow function??? Kid’s Health website http://kidshealth.org/PageManager.jsp?lic=1&article_set=59295&cat_id=20607